Radar question

[Delta59R]

Let me setup a for example scenario, practicing BVR with F-16 AI. 4xphoenix, 4xaim9s. Jester notifies me of bogy contact, I tell him to lock on, we get lock at 70 miles out. I launch a Phoenix at 30 miles out and shortly after the F-16 goes evasive. OK this is where I head scratch- I lose radar contact at say around 20 miles out from evasive maneuvers but a quick switch to SW shows him locked up??… switch back to PH nothing....., switch back to SW got lock, what's going on here? Thanks